Aqueous suspension formulations have been conventionally known as formulations containing a solid agricultural chemical active ingredient. Since water is the dispersion medium for these aqueous suspension formulations, they are less toxic, irritating, and have fewer problems of malodor and environmental pollution caused by organic solvents, and thus are advantageous as compared to other formulations using organic solvents.
The aqueous suspension formulations are prepared by grinding a solid agricultural chemical active ingredient into a powder having an average particle size of about 0.5 μm to 10 μm, mixing the powder with a surface active agent and, if necessary, a water soluble polymer or the like by using water as the dispersion medium, and stabilizing the mixture in the form of a suspension. The water soluble polymer used in this process is a thickening agent for adjusting the viscosity of the formulations, and anionic water soluble polymers (anionic thickening agent) are widely used.
However, if an anionic thickening agent is used concomitantly with a cationic compound (or an acid) when preparing the aqueous suspension formulations, the problems of the formation of a hard cake due to settling and separation of solid particles and the loss of fluidity due to gelation arise at times.
On the other hand, as the formulations using a nonionic thickening agent such as hydroxyalkyl cellulose, (i) an aqueous suspension formulation containing at least one active ingredient selected from an agricultural chemical active ingredient, an industrial antiseptic and antifungal active ingredient, and a household antiseptic and antifungal active ingredient, a water soluble cellulose ether, silica, and water (Patent Document 1); (ii) a granular agricultural chemical formulation containing an agricultural chemical active ingredient having a solubility of 100 ppm or more in water at 20° C., and hydroxypropyl methyl cellulose and/or methyl cellulose (Patent Document 2); a quick drying germicidal disinfectant formed by adding a hydrophobic hydroxypropyl methyl cellulose derivative, in which a long chain alkyl group is introduced, to a disinfectant composed of alcohols such as ethanol and a germicidal disinfectant (Patent Document 3); (iv) an aqueous suspension formulation formed of an insecticidal active ingredient or the like, a water soluble cellulose ether, and water (Patent Document 4); and the like have been known.
However, in these documents, there is no mention of suspension stability when a cationic pest control active ingredient is added to such compositions.
Patent Document 1: Japanese Unexamined Patent Application, First Publication No. 2004-143117
Patent Document 2: Japanese Unexamined Patent Application, First Publication No. 2003-073201
Patent Document 3: Japanese Unexamined Patent Application, First Publication No. Hei 11-349418
Patent Document 4: Japanese Unexamined Patent Application, First Publication No. Hei 10-306001